1. Field of the Invention
The present invention relates to integrated circuits. More particularly, the present invention relates to system-on-a-chip integrated circuits.
2. The Prior Art
Usually system designers employ multiple analog-to-digital converter (ADC) parts to achieve simultaneous analog signal sampling capability. Some analog ADC integrated circuits, such as the ADuC824 manufactured and sold by Analog Devices, employ a multiplexer before an input buffer as shown in FIG. 1, making it impossible to achieve simultaneous sampling if only one ADC chip is used.
Some ADC integrated circuits, such as the ADS7869 manufactured and sold by Texas Instruments, provide three analog-to-digital converters on one chip, as shown in FIG. 2. The ADS7869 includes three, SAR-type, 12-bit ADCs, and three pairs of sample/hold capacitors, which are connected to ADC1 and ADC2, respectively. A single sample/hold capacitor is connected to ADC3. Each sample/hold input is selected from one of four analog inputs. Up to three on-chip ADCs are needed in order to implement simultaneous sampling for up to three analog inputs.
Analog comparators are usually discrete devices used in mixed-signal systems. Some ADC integrated circuits, such as the ADS7869 manufactured and sold by Texas Instruments, have an on-chip window comparator and sign comparator. The window comparator is used to test if the input voltage is within a certain range and the sign comparator is used, for example, for the position sensor inputs in motor control applications or to measure the sign of the main circuits.